1. Field of the Invention
The invention relates to an apparatus and method for determining whether a reforming catalyst, which reforms a mixture of air and fuel, is degraded.
2. Description of the Related Art
As technology for improving fuel consumption in an engine for a vehicle, an apparatus is known which adds a reformate gas that includes CO and H2 both to fuel to be supplied to the combustion chamber of the engine, as well as to the exhaust gas discharged from the combustion chamber (e.g., JP(A) 2002-54427). This apparatus includes a CO shift catalyst that carries a noble metal on a carrier which has the ability to store oxygen. This CO shift catalyst produces a reformate gas that includes CO and H2 by reforming CO and H2O into H2 and CO2 through a water gas shift reaction.
The CO shift catalyst degrades over time, and as the CO shift catalyst degrades, the concentration ratio of CO to H2 (i.e., the CO/H2 concentration ratio) in the reformate gas produced by the CO shift catalyst changes. The related art therefore calculates the ability of the CO shift catalyst to store oxygen from the oxygen concentration at the fluid inlet and the fluid outlet of the CO shift catalyst. A numerical value indicative of this oxygen storage ability is then used to estimate the CO/H2 concentration ratio of the reformate gas. This CO/H2 concentration ratio of the reformate gas is related to the extent of degradation of the CO shift catalyst. The amount of reformate gas to be added to the fuel injected in the engine and to the exhaust gas discharged from the engine is then set based on this estimated CO/H2 concentration ratio.
In actuality, however, it is not easy to accurately calculate the oxygen storage ability of the catalyst. Moreover, in the example of the related art given above, it is necessary to use a plurality of expensive oxygen sensors in order to calculate the oxygen storage ability of the catalyst. Accordingly, with the related art, it is in effect difficult to easily and accurately determine degradation of the catalyst.